The process of testing ground water for contamination may be time consuming, expensive, and environmentally unfriendly. Often, it is desirable to test ground water for contaminants known as "VOCs," or volatile organic compounds. It has been recognized in the art that polyethylene is permeable to volatile organic compounds, including chlorinated VOCs, benzene, and toluene. In accordance with that recognition, others have developed a process called "diffusion sampling" or "passive sampling." The diffusion sampling process takes advantage of the permeability of polyethylene membranes to water-borne VOC contaminants.
In accordance with this technique, a polyethylene bag or membrane is filled with distilled water, sealed, and lowered into the aquifer to be tested. After a sufficient period of time, the VOC contaminants permeate the membrane. Eventually, equilibrium is established between the VOC concentration in the surrounding ground water and the sample in the membrane. The membrane is then withdrawn and the sample is tested.
Don A. Vroblesky and W. Thomas Hyde document both the technical process and their prior art diffusion sampling device in an article entitled, "Diffusion Samplers as an Inexpensive Approach to Monitoring VOCs in Ground Water," Ground Water Monitoring Review, Summer 1997, pp. 177-184. In that article, the authors further discuss the need for withdrawing a specimen from the diffusion sampler without aeration. Aeration of the specimen would render the sample unusable.
The device disclosed by Vroblesky and Hyde, however, has several apparent drawbacks. That device is difficult to use in the field due to the need to heat seal polyethylene bags which contain water. Further, that device provides no convenient method for withdrawing a specimen. Also, the device has little structure to which tether lines, weights, and the like may be conveniently and securely attached.
It is readily apparent that an improved diffusion sampling device is needed to overcome the drawbacks apparent in the prior art, and to render more convenient the diffusion sampling method for the testing of ground water. It is, therefore, to the provision of such an improved diffusion sampling device that the present invention is directed.
Accordingly, the several objects of the present invention are:
to provide an improved diffusion sampler having convenient and reliable means to seal the device against leakage; PA1 to provide an improved diffusion sampler having convenient and reliable means for filling, weighting, lowering, and recovering the device; PA1 to provide an improved diffusion sampler having convenient and reliable means for extracting a test specimen, without degradation, from within the device; PA1 to provide an improved diffusion sampler which will resist deterioration through abrasion; PA1 to provide an improved diffusion sampler which is structurally reinforced against the mechanical stresses of the sampling environment; PA1 to provide an improved diffusion sampler which is reusable for multiple tests, yet may also be disposable at the end of its useful service life; and, PA1 to provide an improved diffusion sampler which is economical to manufacture, and which is simple and convenient to use under typical field conditions.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art by reference to the drawings and to the detailed description of the preferred embodiment presented herein.